The Filet-O-Fish was introduced nationally in the United States in 1965.
McDonald’s franchisee Lou Groen developed the sandwich in Cincinnati, where many Catholic customers avoided meat on Fridays. The fish sandwich gave restaurants an alternative menu item during a period when religious eating customs affected Friday sales.
The original sandwich used a breaded fish fillet, tartar sauce, and cheese on a bun. Its success led McDonald’s to add it nationally, and it became one of the company’s enduring named products.
The Filet-O-Fish is sometimes dated only to its regional test, which began before the national rollout. The key branding milestone is 1965, when McDonald’s made the product available across the United States. Fish species and preparation details have changed in different markets and eras.